Toward a standardised protocol for the stable isotope analysis of scleractinian corals.

RATIONALE: The stable isotope analysis of carbon and nitrogen is a powerful tool in many ecological studies, but different sample treatments may affect stable isotope ratios and hamper comparisons among studies. The goal of this study was to determine whether treatments that are commonly used to prepare scleractinian coral samples for stable isotope analysis yield different δ15 N and δ13 C values, and to provide guidelines toward a standardised protocol. METHODS: The animal tissues and Symbiodiniaceae of two symbiotic scleractinian coral species (Stylophora pistillata and Porites lutea) were divided into subsamples to test the effects of the drying method, lipid extraction, acidification treatment and water washing. All the subsamples were analysed for their δ15 N and δ13 C values, using continuous flow elemental analyser/isotope ratio mass spectrometry. RESULTS: The drying method and lipid extraction treatment had no substantial effects on the δ15 N and δ13 C values of Symbiodiniaceae and animal tissues. Acid treatment did cause significant differences in δ13 C values (mean differences ≤0.5‰, with individual samples becoming up to 2.0‰ more negative), whereas no ecologically significant differences were observed in δ15 N values. Animal tissue δ13 C values may vary depending on whether samples are washed or not. CONCLUSIONS: To move towards a standardised protocol in coral research, we recommend using an available drying method (as they are equally acceptable) for the stable isotope analysis of scleractinian corals, examining the need for lipid extraction on a case-by-case basis, performing a direct acidification of Symbiodiniaceae and animal tissues, and avoiding washing animal tissue with distilled water.

Ecomorphology, trophic niche, and distribution divergences of two common damselfishes in the Gulf of California.

Damselfishes of the genus Stegastes are among the most conspicuous benthic reef-associated fish in the Gulf of California, and the two most commonly found species are the Beaubrummel Gregory Stegastes flavilatus and the Cortez damselfish Stegastes rectifraenum. Both species are described as ecologically and morphologically very similar. However, the niche theory predicts that coexisting species will tend to minimize competition through niche partitioning. We, therefore, investigated the degree of their ecological similarity through their morphology, trophic ecology, and spatial distribution, as well as, the effects of environmental variables on their abundance. We showed that S. rectifraenum is highly abundant in the entire Gulf of California while S. flavilatus is only found in the central and southern part. The abundance of S. rectifraenum was higher in shallow water and decreased when the cover of macroalgae and sand increased. No environmental variable was related to the abundance of S. flavilatus. Both species had distinct isotopic niches: S. flavilatus fed almost exclusively on plankton and zoobenthos, while S. rectifraenum had an omnivorous diet mixing turf, zoobenthos and plankton. The diet divergence was reflected in the morphology of the two species. Stegastes flavilatus had a more rounded body shape, with a higher supraoccipital crest and more gill rakers than S. rectifraenum, which may increase its ability to feed on vagile invertebrates and zooplankton. Our results support the hypothesis that a niche partition has occurred between the two species. Furthermore, the importance of planktonic food sources to both species, considered as benthic territorial feeders, challenges the traditional ecological description of the Stegastes species.

The dark side of the black caiman: Shedding light on species dietary ecology and movement in Agami Pond, French Guiana.

The black caiman is one of the largest neotropical top predators, which means that it could play a structuring role within swamp ecosystems. However, because of the difficulties inherent to studying black caimans, data are sorely lacking on many aspects of their general biology, natural history, and ecology, especially in French Guiana. We conducted a detailed study of the Agami Pond black caiman population using a multidisciplinary approach. The aim was to better understand the species' dietary ecology and movements in the pond, and thus its functional role in pond system. We gathered natural history data, tracked caiman movements using satellite transmitters, and characterized feeding ecology via stable isotope analysis. Our study was carried out over three sampling periods and spanned both wet and dry seasons, which differ in their hydrological and ecological conditions. Our results show that black caiman abundance and age demographics differed between seasons in Agami Pond. In the dry season, Agami Pond is one of the only areas within the marsh to hold water. It thus contains large quantities of different fish species, which form the basis of the black caiman's diet. Caiman body size, a proxy for age class, was around 1.5 meters. During the wet season, which corresponds to the breeding period for migratory birds (e.g., Agami herons), adult black caimans are present in Agami Pond. Adults were most abundant in the inundated forest. There, most individuals measured up to 2 meters. They also exhibited a particular "predatory" behavior near bird nests, preying on fallen chicks and adults. Juveniles and subadults were present during both seasons in the pond's open waters. These behavioral observations were backed up by stable isotope analysis, which revealed ontogenetic variation in the caiman's isotopic values. This isotopic variation reflected variation in diet that likely reduced intraspecific competition between adults and young. The telemetry and microchip data show that different age classes had different movement patterns and that seasonal variation in the pond may influence caiman prey availability and reproductive behavior. The new information gathered should help predict this species' responses to potential ecosystem disturbance (e.g., water pollution, habitat destruction) and inform the development of an effective conservation plan that involves locals and wildlife officials.

Using an apex predator for large-scale monitoring of trace element contamination: Associations with environmental, anthropogenic and dietary proxies.

Understanding the levels and drivers of contamination in top predators is important for their conservation and eventual use as sentinels in environmental monitoring. Therefore, metals and trace elements were analyzed in feathers of Bonelli's eagles (Aquila fasciata) from southern Portugal in 2007-2013, where they are believed to be exposed to a wide range of contamination sources such as agricultural land uses, urban areas, active and abandoned mines and a coal-fired power plant. We focused on concentrations of aluminum (Al), arsenic (As), copper (Cu), chromium (Cr), mercury (Hg), lead (Pb), selenium (Se) and zinc (Zn), as these contaminants are potentially associated with those sources and are known to pose a risk for terrestrial vertebrates. Stable isotope values of nitrogen (δ15N: 15N/14N), carbon (δ13C: 13C/12C) and sulphur (δ34S: 34S/32S) were used as dietary proxies to control for potential effects of prey composition on the contamination pattern. The spatial distribution of potential contamination sources was quantified using geographic information systems. Concentrations of Hg in the southern part of the study area were above a reported toxicity threshold for raptors, particularly in territories closer to a coal-fired power plant at Sines, showing that contamination persisted after a previous assessment conducted in the 1990s. Hg and Se levels were positively correlated with δ15N, which indicates biomagnification. Concentrations of As, Cr, Cu, Pb and Zn were generally low and unrelated to mining- or industrial activities, indicating low environmental background concentrations. Al was found at higher concentrations in the southernmost areas of Portugal, but this pattern might be related to external soil contamination on feathers. Overall, this study indicates that, among all elements studied, Hg seems to be the most important contaminant for Bonelli's eagles in southern Portugal, likely due to the power plant emissions and biomagnification of Hg in terrestrial food webs.

Biogeography of functional trait diversity in the Taiwanese reef fish fauna.

The richness of Taiwanese reef fish species is inversely correlated to latitude as a direct consequence of the abiotic environment and its effects on benthic habitats. However, to date, no studies have investigated the variations in the diversity of traits (FD) linked with the role of these fishes in the ecosystem. FD is usually considered more sensitive than species richness in detecting early changes in response to disturbances, and therefore could serve as an indicator of ecological resilience to environmental changes. Here, we aim to characterize FD in the Taiwanese reef fish fauna and to document its regional variations. Six traits were used to categorize the 1,484 reef fish species occurring in four environmentally contrasted regions around Taiwan. The number of unique trait combinations (FEs), their richness (FRic), their redundancy (FR), their over-redundancy (FOR), and their vulnerability (FV) were compared among these regions. Overall, 416 FEs were identified. Their number decreased from south to north in step with regional species richness but FRic remained similar among regions. FR and FOR were higher to the south. At the local scale, variations in FEs and FRic are in concordance with the worldwide pattern of FD. High-latitude, impoverished fish assemblages, offer a range of trait combinations similar to diversified tropical assemblages. Increasing diversity in the latter mainly contributes to raising FR and supports already over-redundant entities. High vulnerability makes many combinations highly sensitive to species loss, and was higher at intermediate latitudes when using a fine resolution in trait categories. It suggests that the loss of FEs may first be characterized by an increase in their vulnerability, a pattern that could have been overlooked in previous global scale analyses. Overall, this study provides new insights into reef fish trait biogeography with potential ramifications for ecosystem functioning.

Mercury Stable Isotopes Discriminate Different Populations of European Seabass and Trace Potential Hg Sources around Europe.

Our study reports the first data on mercury (Hg) isotope composition in marine European fish, for seven distinct populations of the European seabass, Dicentrarchus labrax. The use of δ202Hg and Δ199Hg values in SIBER enabled us to estimate Hg isotopic niches, successfully discriminating several populations. Recursive-partitioning analyses demonstrated the relevance of Hg stable isotopes as discriminating tools. Hg isotopic values also provided insight on Hg contamination sources for biota in coastal environment. The overall narrow range of δ202Hg around Europe was suggested to be related to a global atmospheric contamination while δ202Hg at some sites was linked either to background contamination, or with local contamination sources. Δ199Hg was related to Hg levels of fish but we also suggest a relation with ecological conditions. Throughout this study, results from the Black Sea population stood out, displaying a Hg cycling similar to fresh water lakes. Our findings bring out the possibility to use Hg isotopes in order to discriminate distinct populations, to explore the Hg cycle on a large scale (Europe) and to distinguish sites contaminated by global versus local Hg source. The interest of using Hg sable isotopes to investigate the whole European Hg cycle is clearly highlighted.

A functional approach to the structural complexity of coral assemblages based on colony morphological features.

Colony morphological features is among the best predictor of the scleractinian coral's function in reef ecosystems. However, morphological traits are categorical and to convert this information into a quantitative value as well as estimate their influence on ecosystem process remain a challenge. Here, we propose a trait-based approach to quantify morphological diversity and assess the structural complexity of the habitat provided by corals. We used a previously published dataset that is related to a bleaching event that affected the coral reef off Tikus Island in Indonesia in 1983. We found clear signs of recovery of the coral assemblage's complexity toward pre El Niño conditions five years after the event. Independent of the change observed in species richness, this return in structural complexity was accompanied by a global decrease in species number associated with each particular morphological entity (Functional Redundancy) and an increase in the number of single-species entities (Functional Vulnerability). Together with species loss, we show an overall functional erosion of the coral assemblage and suggest that the role of the coral reef habitat could be strongly imperiled under repeated or synergistic disturbances. This approach offers an opportunity for a better understanding of coral responses to natural and anthropogenic disturbances.

Carbon, nitrogen and sulphur isotopic fractionation in captive juvenile hooded seal (Cystophora cristata): Application for diet analysis.

RATIONALE: Intrinsic biogeochemical markers, such as stable isotope ratios of carbon, nitrogen and sulphur, are increasingly used to trace the trophic ecology of marine top predators. However, insufficient knowledge of fractionation processes in tissues continues to hamper the use of these markers. METHODS: We performed a controlled feeding experiment with eight juvenile hooded seals (Cystophora cristata) that were held on a herring-based diet (Clupea harengus) for two years. Stable isotope ratios were measured via isotope ratio mass spectrometry in three of their tissues and related to values of these markers in their diet. RESULTS: Diet-tissue isotope enrichment (trophic enrichment factor, TEF) values between dietary herring and seal tissues for carbon (Δ13 C) were +0.7 ‰ for red blood cells, +1.9 ‰ for hair and +1.1 ‰ for muscle. The TEFs for nitrogen trophic (Δ15 N) were +3.3 ‰ for red blood cells, +3.6 ‰ for hair and +4.3 ‰ for muscle. For sulphur, the Δ34 S values were +1.1 ‰ for red blood cells, +1.0 ‰ for hair and +0.9 ‰ for muscle. CONCLUSIONS: These enrichment values were greater than those previously measured in adult seals. This increase may be related to the higher rate of protein synthesis and catabolism in growing animals. This study is the first report on sulphur isotope enrichment values for a marine mammal species.

Isotopic half-life and enrichment factor in two species of European freshwater fish larvae: an experimental approach.

RATIONALE: Stable isotope ratios of carbon and nitrogen are valuable tools for field ecologists to use to analyse animal diets. However, the application of these tools requires knowledge of the tissue enrichment factor (TEF) and half-life (HL). We experimentally compared TEF and HL in two freshwater fish larvae. We hypothesised that chub had a better growth/tissue replacement ratio than roach, due to the use of a food closer to their natural diet. METHODS: We determined the isotopic HL, the TEF and the contribution of growth or metabolic tissue replacement to dynamic isotopic incorporation. After yolk sac resorption, larvae were fed for 5 weeks with prey similar to their natural diet (Artemia nauplii) up to the isotopic equilibrium followed by Chironomid larvae. Stable isotope measurements were carried out using a continuous flow isotope ratio mass spectrometer coupled to an elemental analyser. RESULTS: Changes in isotopic composition strongly followed the predictions of exponential growth and time-dependent models. The isotopic HL varied between 8.2 and 12.6 days and the TEF of nitrogen and carbon ranged from 1.7 to 3.1 ‰ and from -0.9 to 1.2 ‰, respectively. The incorporation of dietary 13 C was due more to the production of new tissue (between 56 and 79%) than to the metabolic process. Chub allocated more energy to growth than roach and the Chironomidae diet contributed more to the consumers' growth than the Artemia diet. CONCLUSIONS: Metabolic rates seemed lower for chub than for roach, especially when they were fed with Chironomidae. A Chironomidae-based diet would be more profitable to chub, and the high associated growth rate could increase the development of the fish larvae. The HL and TEF were in the range of those reported in the literature. These results will be helpful for field-based studies, because they can help to increase the accuracy of models. Copyright © 2017 John Wiley & Sons, Ltd.

Extreme intra-clutch egg size dimorphism is not coupled with corresponding differences in antioxidant capacity and stable isotopes between eggs.

Oviparous females need to allocate resources optimally to their eggs in order to maximize their fitness. Among these resources, dietary antioxidants, acquired by females and transferred to the eggs during egg formation, can greatly affect the development and survival of the embryo and chick. In crested penguins, incubation starts after the second and last egg is laid and, as opposed to many other bird species, this egg hatches first, thereby enhancing the survival of the chick. Here, we assessed whether antioxidant and isotopic composition could underlie these differences between eggs within clutches of southern rockhopper penguins (Eudyptes chrysocome chrysocome). The second-laid egg had higher total antioxidant capacity than the first-laid egg, although this was not due to higher antioxidant concentration but to its higher mass. This suggests that resources are allocated by females at a constant rate in both eggs within clutches. Accordingly, we found a strong correlation for isotopic compositions between eggs suggesting that resources were allocated similarly to each egg within the clutch. Overall, we found little evidence for a significant role of antioxidant and isotopic compositions to explain differences in terms of embryo/chick development between eggs in crested penguins. However, since our results suggest a constant rate of antioxidant transfer from females to eggs, limiting the mass of the first-laid egg might represent a strategy for females to spare antioxidant defences and preserve self-maintenance.

AxIOM: Amphipod crustaceans from insular Posidonia oceanica seagrass meadows.

BACKGROUND: The Neptune grass, Posidonia oceanica (L.) Delile, 1813, is the most widespread seagrass of the Mediterranean Sea. This foundation species forms large meadows that, through habitat and trophic services, act as biodiversity hotspots. In Neptune grass meadows, amphipod crustaceans are one of the dominant groups of vagile invertebrates, forming an abundant and diverse taxocenosis. They are key ecological components of the complex, pivotal, yet critically endangered Neptune grass ecosystems. Nevertheless, comprehensive qualitative and quantitative data about amphipod fauna found in Mediterranean Neptune grass meadows remain scarce, especially in insular locations. NEW INFORMATION: Here, we provide in-depth metadata about AxIOM, a sample-based dataset published on the GBIF portal. AxIOM is based on an extensive and spatially hierarchized sampling design with multiple years, seasons, day periods, and methods. Samples were taken along the coasts of Calvi Bay (Corsica, France) and of the Tavolara-Punta Coda Cavallo Marine Protected Area (Sardinia, Italy). In total, AxIOM contains 187 samples documenting occurrence (1775 records) and abundance (10720 specimens) of amphipod crustaceans belonging to 72 species spanning 29 families. The dataset is available at http://ipt.biodiversity.be/resource?r=axiom.

Is individual consistency in body mass and reproductive decisions linked to individual specialization in foraging behavior in a long-lived seabird?

Individual specialization in diet or foraging behavior within apparently generalist populations has been described for many species, especially in polar and temperate marine environments, where resource distribution is relatively predictable. It is unclear, however, whether and how increased environmental variability - and thus reduced predictability of resources - due to global climate change will affect individual specialization. We determined the within- and among-individual components of the trophic niche and the within-individual repeatability of δ(13)C and δ(15)N in feathers and red blood cells of individual female southern rockhopper penguins (Eudyptes chrysocome) across 7 years. We also investigated the effect of environmental variables (Southern Annular Mode, Southern Oscillation Index, and local sea surface temperature anomaly) on the isotopic values, as well as the link between stable isotopes and female body mass, clutch initiation dates, and total clutch mass. We observed consistent red blood cell δ(13)C and δ(15)N values within individuals among years, suggesting a moderate degree of within-individual specialization in C and N during the prebreeding period. However, the total niche width was reduced and individual specialization not present during the premolt period. Despite significant interannual differences in isotope values of C and N and environmental conditions, none of the environmental variables were linked to stable isotope values and thus able to explain phenotypic plasticity. Furthermore, neither the within-individual nor among-individual effects of stable isotopes were found to be related to female body mass, clutch initiation date, or total clutch mass. In conclusion, our results emphasize that the degree of specialization within generalist populations can vary over the course of 1 year, even when being consistent within the same season across years. We were unable to confirm that environmental variability counteracts individual specialization in foraging behavior, as phenotypic plasticity in δ(13)C and δ(15)N was not linked to any of the environmental variables studied.